1. Field of the Invention
The present invention relates to a battery comprising a cathode, an anode, and an electrolyte, and more particularly such a battery whose anode has an anode collector and an anode active material layer.
2. Description of the Related Art
In recent years, in connection with high-performance and multi-function of mobile devices, high capacities of secondary batteries, the power source for the mobile devices have been desired earnestly. As a secondary battery which meets this demand, there is a lithium secondary battery. However, in the case of using cobalt acid lithium for a cathode and graphite for an anode, which is currently a typical form for lithium secondary batteries, a battery capacity is in a saturated state, and it is extremely difficult to greatly obtain a high capacity of the battery. Therefore, from old times, using metal lithium (Li) for an anode has been considered. However, in order to put this anode to practical use, it is necessary to improve efficiency of precipitation dissolution of lithium and to control dendrite precipitation form.
Meanwhile, a high capacity anode using silicon (Si), tin (Sn) or the like has been actively considered. However, when charge and discharge are repeated, these anodes are pulverized and miniaturized due to significant expansion and shrinkage of an anode active material, collecting characteristics are lowered, and decomposition reaction of an electrolyte solution is facilitated due to an increased superficial area, so that their cycle characteristics are extremely poor. Therefore, an anode wherein an anode active material layer is formed on an anode collector by vapor-phase method, liquid phase method, sinter method and the like has been considered (for example, refer to Japanese Unexamined Patent Application Publication No. H08-50922, Japanese Patent No. 2948205, and Japanese Unexamined Patent Application Publication No. H11-135115). According to this anode, since miniaturization can be inhibited compared to conventional application type anodes wherein slurry containing a particulate anode active material and a binder is applied, and the anode collector and the anode active material layer can be integrated, so that electronic conductivity in the anode becomes extremely excellent, and high performance in terms of capacity and cycle life is expected. In addition, a conductive material, a binder, and voids which have existed in the anode conventionally can be reduced or excluded. Therefore, the anode can become a thin film essentially.
However, even in the anode wherein the anode active material layer is formed on the anode collector by vapor-phase method, liquid phase method, or sinter method, there is a problem that a film formed on the surface of the anode active material layer is not stabilized due to expansion and shrinkage of the anode active material associated with charge and discharge, so that continuous decomposition reaction of the electrolyte solution is induced. Therefore, even in this case, it is difficult to say that its cycle characteristic are sufficient. That is, it is necessary that more stable and stronger film is formed on the surface of the anode active material layer.